Clutch control mechanism



April 1941. P. H. MAURER 2 CLUTCH CONTROL MECHANISM Filed July 19, 19374 Sheets-Sheet 1 Ci iaw BY r 6 J ATTiR/vEJ Z.

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Patented Apr. 8, 1941 CLUTCH CONTROL MECHANISM Paul H. Maurer,Birmingham, Mich, assignor to Hudson Motor Car Company, Detroit, Mich, a

corporation of Michigan Application July 19, 1937, Serial No. 154,356

Claims.

This invention relates to motor vehicles and .more particularly toclutch control devices therefor designed generally for the purpose ofautomatically disengaging the clutch, when the accelerator pedal isreleased, in order to disconnect the driving wheels of a vehicle fromthe engine.

thereof, thereby effecting free wheeling" operation of the vehicle andpermitting shiftin the gears without manually operating the clutchpedal.

Devices of the foregoing character utilize the increase of vacuum in theintake manifold of the vehicle engine produced by the pumping action ofthe engine and by the restriction of the intake passage thereof by thethrottle valve when the accelerator pedal is released by the driver.Such devices commonly comprise a cylinder having a slidable pistontherein connected with the aid of a suitable leverage with the clutchoperating mechanism, means being provided to connect the cylinder at oneside of the piston with the intake manifold of the engine, therebypermitting the manifold vacuum to act upon said piston and the leverageconnected therewith, moving the same into position to effectdisengagement of the clutch.

In practice it has been found that free wheeling of a vehicle isundesirable and in fact dangerous when the speed of the vehicle exceeds,for example, twenty-five or thirty miles per hour.

This is largely due to the fact that when free at relatively high speed.This also results in greatly increased wear of the brake linings.

As a consequence, in the use of power plants I utilizing vacuumtypeautomatic clutch control it has been desirable to provide means wherebythe automatic disengagement of the clutch during deceleration would belimited to vehicle speeds below a certain predetermined speed, such forexample as twenty miles per hour, in order that braking effect of theengine could be retained at higher vehicle speeds. Several devicesintended to perform the functions described have been devised.

In accordance with present usage a centrifugal governing device orswitch similar in construction to a conventional centrifugal governor isemployed for this purpose. In such devices the centrifugal forceproduced by rotating a plurality of weights is utilized to.control amember adapted to interrupt the vacuum connection between the intakemanifold and the vacuum operated cylinder, thereby rendering the clutchoperating piston inoperative. However, numerous inherent disadvantageshave been found in the centrifugal switches, and their use incombination with motor vehicles has presented numerous difficulties. Oneof such difficulties has been due to the fact that centrifugal switchesmust operate at low speeds and therefore they necessarily includerelatively large masses. As the speed of the vehicle increases, theinertia force sg developed in a device of this type reach suchmagnitudes that objectionably high loads are imposed on the switch partsas well as on the speedometer worm and gear from which the switch isusually driven. Another source of difflculties resides in the fact thatwith the clutch controls of the prior designs the clutch cannot bedisengaged quickly enough to prevent stalling of the engine at a suddenapplication of brakes. The above made driving in traflic very difficultand was responsible for discharge of batteries.

In practice it has been found necessary to set centrifugal switches tooperate and cause free wheeling at what in some cases may be anundesirably high speed. In addition, the inherent tendency ofcentrifugal governing devices to hunt" before coming into a balancedposition has complicated the problem still further, making the use ofcentrifugal switches in clutch control devices unsatisfactory.

It is one of the objects of the present invention to provide an improvedclutch control device for a'motor vehicle, which ensures automaticdisengagement of the clutch when the accelerator pedal is released.

Another object of the invention is to provide improved means whichrender the automatic clutch disengaging means inoperative when thevehicle operated in high gear reaches a predetermined maximum speed,thereby preventing dangerous free wheeling at high vehicle speeds.

A further object of the invention is to provide improved clutch controlmeans which effect a more satisfactory disengagement of the clutchbefore the vehicle is brought to a stop by application of the brakes.

A still further object of the invention is to provide a control switchwhich is very easy to actuate, and yet which is quickly responsive andcomes into the proper position without hesitation or hunting.

It is an added object of the invention to provide an improved clutchcontrol device of the foregoing character, which is relatively simple inconstruction and dependable in operation, and which is relatively cheapto manufacture and is easy to service or repair.

Other objects of this invention will appear in the following descriptionand appended claims,

. reference being had to the accompanying drawings forming'a part ofthis specification wherein like reference characters designatecorresponding parts in the several views.

Fig. 1 is a side view, partly in section, of a vehicle engine embodyingthe present invention, the electrical circuit being diagrammaticallyshown thereon, illustrating driving conditions in low gearswith theautomatic clutch operating.

Fig. 2 illustrates the conditions which occur when the vehicle is beingaccelerated in low gears. v

Fig. 3 is a view similar in part to that of Fig. 1, illustratingconditions when the vehicle is just shifted into high gear. I

Fig. 4 shows the conditions occurring when the vehicle operated in highgear is being stopped by a sudden application of brakes.

Fig. 5 is a diagrammatic view ofthe electric circuit controlling thesolenoid valve, the same being shown separate from the engine for thesake of clarity.

Fig. 6 is a side view of the wind switch included in the electriccircuit and controlling the same under certain conditions.

Fig. 7 is a front view of the switch shown in Fig. 6.

Fig. 8 is a view similar in part to that of Fig. 6, the switch beingshown in its closed position.

Fig. 9 is a perspective view of a modified wind switch embodying thepresent invention.

Fig. 10 is a view taken in the direction of the arrows on the linelfl-IOof Fig. 9.

Fig. 11 is a side view of the wind switch of Fig. 9, the same beingshown in its closed position, dotted lines indicating the respectivepositions of the switch parts when the same is in its open position.

Fig. 12 is a top view fllustrating the wind switch of Fig. 9, the upperpart of the vane being removed along the line |2-l2 of Fig. 11 in ordernot to obscure the working parts of the switch mechanism.

Before explaining in detail the present invention it is to be understoodthat the invention is not limited in its application to the details ofconstruction and arrangement of parts illustrated in the accompa y ngdrawings, since the invention is capable of otherembodiments and ofbeing practiced or carried out in various ways. Also it is to beunderstood that the phraseology or terminology employed herein is forthe purposevof description and not of limitation, and it is not intendedto limit the invention claimed herein beyond the requirements of theprior art.

In the drawings there is illustrated, by way of example, a motor vehiclepower plant embodying the present invention. With reference particularlyto Figs. 1 to 4, the numeral indicates generally an internal combustionengine of any desirable type having an intake manifold 2|. At

the rear end of the engine 20 there is provided a clutch mechanism whichcomprises a flywheel 22 secured to the rear end of the engine crankshaft22. The bell housing 24 carries a plurality of compression springs 25bearing upon a pressure plate 26 drivingly connected with the flywheel22 by means of studs 21. The rear face of the flywheel 22 and the frontface of the pressure plate 26 are adapted to bear against the faces of adriving plate 28 provided with suitable frictional surfaces. The drivingplate 28 is drivingly connected with a transmission shaft 29, while thepressure plate 28 and the flywheel 22 are free to rotate independentlyof the transmission shaft but are constrained to rotate with thecrankshaft 23, as explained. Thus, when the plate 26 comes in contactwith the drive plate 28, pressing the same against the rear face of theflywheel 22, a frictional driving connection is effected between thecrankshaft 22 and the transmission shaft 22.

Means are provided for the purpose of effecting disengagement of theabove described driving connection between the crankshaft and thetransmission shaft, which means in the present embodiment of theinvention comprise a clutch throwout finger I! fulcrumed between itsends, one end being pivotally connected at II to the pressure plate 20while its other end bears against a shiftable collar 32. It is obviousthat pressing the collar 32 .forward will result in drawing the pressureplate back from the driving plate 28, thus releasing the frictionalconnection between the crankshaft and the trans mission shaft. Forpressing the collar 22 forward as described, there is provided a clutchshifter yoke 33 rockably mounted on the shaft 34. Means are providedwhereby the yoke 22 presses the collar 32 forward as the clutch pedal(not shown) is pressed down by the driver of the vehicle. Thedescription of said means is omitted since they do not form a part ofthe present invention and may be of any suitable type.

Automatic disengagement of the clutch is effected by means of a powercylinder 25 suitably supported, a conduit 32 connecting the powercylinder with the intake manifold of the engine, and a suitable linkageoperated by the power cylinder. Within the cylinder 26 there is slidablyfitted a piston 21 having a piston rod 2| connected by means of a hingedrock arm 29 and a rod 40 with the clutch shifter yoke 32. It can beclearly seen from an examination of the drawings that if communicationis effected between the intake manifold 2| and the front end of thepower cylinder 35 under conditions when there is a vacuum in the intakemanifold, the

piston 31 will be drawn forwardly until it reaches the end of thecylinder. Forward movement of the piston 31 operates the rock arm 39 andthe rod 40, in consequence whereof the yoke 35 presses the collar 32forward and disengages the clutch. Since the vacuum in the intakemanifold is particularly strong when the accelerator pedal of thevehicle is in released position, it will be appreciated thatdisengagement of the clutch when the engine is idling is effected in avery strong and positive manner.

In order to prevent disengagement of the clutch in conditions other thanidling, means are provided to interrupt under suchconditions the vacuumconnection between the intake manifold 2i and the power cylinder 35.Said means are exemplified by a valve device interposed in the vacuumconduit 38 and comprising a cylinder 4| in which there is slidablyfitted a recessed valve 42 connected by means of suitable leverage andlinkage with the accelerator pedal 43. Ports Ma and lib are provided inthe valve cylinder 4| and they communicate with the conduit 30.

The linkage connecting the accelerator pedal 43 and the valve 42 is soarranged that when the accelerator pedal is released (Fig. 1) the recess42a of the valve 42 is positioned right against the ports a and lib and,therefore, the communication of the intake manifold and the powercylinder is not interrupted and the vacuum is permitted to act on thepiston 31. As the accelerator pedal is pressed down, the valve 42 movesinto the position shown in Fig. 2, interrupting communication betweenthe intake manifold and the power cylinder. Under these conditions thesprings 25 will operate to means are provided to interrupt thecommunimum speed at which the automatic clutch disengaging means arepermitted to operate. Above the speed of twenty miles per hour automaticoperation of the clutch disengaging means ceases,

and conventional operation or the-clutch is reestablished. This featureof the invention elim inates any possible danger of automaticallydisengaging the clutch at higher vehicle speeds.

In the present embodiment of the invention, said means are exemplifiedbyte. solenoid operated valve indicated generally by thenumeral 44.Referring to the drawings the solenoid valve comprises a casing 45provided on the valve cylinder II at the port 4la thereof andcommunicating with the extension 46a of the vacuum conduit 36. In thepresent instance the casing 45 is formed integrally with the valvecylinder H. In the casing 45 there is operatively arranged a solenoidoperated valve 46 which is normally adapted to close the port 4Ia,thereby interrupting the continuity of the vacuum conduit 36, theclosing of said valve being caused by the pressure spring 41.

In order to produce the desired operation of the automatic clutch thevalve 44 should be open when the vehicle is operated in low gears, suchas in first, second and reverse gears, and under such conditions thevalve 42 alone controls the automatic clutch control means. When,.however, the gears are shifted and the vehicle is being operated inhigh gear, the valve 44 should be kept open permitting the valve 42 tocontrol the vacuum conduit only up to the predetermined speed, such astwenty miles per hour, at which speed the valve 46-should closerenderingthe valve 42 inoperative to control said vacuum conduit at any speedabove said predetermined speed.

In the present embodiment of the invention such operation of the valve46 is attained with the aid of an electric circuit indicated in Figs. 1to 5 inclusive. The circuit comprises a source of electric energy 50,such for instance as a storage battery; one of the terminals of which isgrounded on the vehicle structure as indicated at 5|, while there is aconductor 52 connected to the other terminal of said source 40. A switch53 is mechanically connected with the ignition switch (not shown) inorder to prevent unnecessary discharging of the source when the vehicleis not operating. The conductor 52 is electrically connected with asolenoid winding 44, the stem 46a of the valve 46 serving as an armaturefor said winding. The other end of said winding is connected to aconductor 55 leading to the high gear switch 54 mounted on thetransmission casing. The high gear switch 56', when closed, is groundedon the vehicle structure as indicated at 51. During operation of thevehicle in high gear this switch 56 remains open and is only closed toground the same by the high gear shift rail when operated to shift outor high gear. When the switches 53 and 58 are closed, the electriccurrent flows from one of the terminals of the source through theconductor '42,

winding 44, conductor 45, high gear switch 54 and through the groundpoints 51 and iii back to the source 50. The flow of current through thewinding 44 produces a magnetic field around the valve stem 46a, sumcientto pull the valve 44 up in opposition to the action of the spring 4Ithereby opening the valve 45. Such condition is illustrated in Fig. 1.

If, however, the above described circuit is opened at either of theswitches 53 or 56 the flow of the electric current ceases and thesolenoid is deenergized, in consequence whereof the spring 41 pressesthe valve 46 down to close the port 41a, thereby interrupting the vacuumcommunication.

Means for opening the valve 46 when the vehicle is being operated inhigh gear and travels at or below the predetermined speed, such as anyspeed not exceeding twenty miles per hour, are exemplified by a parallelcircuit or a subcircuit connected to the conductor at a point 40 andincluding a wind switch 6|, one 01 the terminals whereof is electricallyconnected through a conductor with the conductor 55 at point 60, whilethe other terminal is grounded on the vehicle structure as indicated at42.

In the present embodiment of the invention the wind switch is operatedby the air stream produced by the fan 63 driven from the enginecrankshaft by means of a belt 44. The switch is of the vane-type and,therefore, the energy of velocity of the stream is depended upon ioractuating the switch. It will be understood, however, that the inventionis not limited to the velocity type oi vane, and theta switch includinga pressure responsive membrane may be constructed in accordance with theinvention. Since the speed of the vehicle in a definite gear, the highgear in the present instance, is proportional to the rotative speed ofthe engine, the velocity of the air-in the stream produced by the Ian-43is also substantially proportional to the speed of the vehicle, andthere is a certain velocity of the air in the stream that corresponds tothe vehicle speed of twenty miles per hour.

The vane 44 o! the switch is mounted on a shaft 84 journalled in acasing 61 suitably supported on the engine structure and in such alocation that the vane 44 is arranged transversely to the direction ofthe air flow. The action of the air stream tends to throw the vanetoward the rear of the vehicle, turning the vane on the shaft 44, whichmovement of the vane is opposed by the spring 44 anchored to the casingby one of its ends while its opposite end engages one o! the notches 44provided on the cam 10 mounted on the shaft 44 and constrained to rotatetherewith.

The resistanceoi' the spring 68 may be changed by moving the end of thespring 48 into any desired notch of the series of notches 68, therebychanging the resistance which the vane 45 oflers to the air stream. Inthe present embodiment the tension of the spring 44 and the area of thevane 45 are so selected that the vane 64 will not move until thevelocity of the air in the stream reaches the value corresponding to thepredetermined speed of the vehicle, such as twenty miles per hour. Whensaid speed is reached, the vane is thrown rearward and the contact stripH is drawn away from the contact piece 12 breaking the circuit at thepoint where the strip II and cured on the casing 61. It is an importantfeature of the present invention that movement of the vane 65 andopening or closing of the switch is effected practically momentarily andwithout objectionable hesitation. Means effecting such movement of thevane 65 are exemplified in the present embodiment by a compressionspring suitably supported on the casing 61 and operating to press thefollower 18 against the cam 10. A cam portion 11 cooperating with thefollower 16' is so shaped that pressure of the follower produces astrong snappy movement of the vane 65' after it reaches its middleposition, it being understood that the contact piece II is resilient andis so bent that it maintains the contact with the piece 12 until thevane 35 reaches said middle position. there is produced a sharp line ofseparation between the speeds of the vehicle causing opening or closingof the wind switch in order to prevent undesirable repeated opening andclosing of the switch when the car is being driven at the critical speedfor a considerable length of time.

Another important feature of the present invention resides in the factthat the vane 65 has a suflicient weight inertia so that when thevehicle stops suddenly or is very rapidly decelerated by the suddenapplication of the brakes, the vane will be thrown forward by inertia tomake contact between members H and 12. It will be understood that suchforward movement of the vane 65 results in closing the wind switch atcontacts II and I2 and completing the circuit therethrough.

It will now be clear in view 01' the foregoing that opening of the valve48 may be eifected in high gear by completing the electric circuit atthe wind switch 6|. It should be noted that in lower gears the circuitis always completed through the high gear switch 56 and that the valve48 will be open irrespective of the position of the wind switch 6|. Onthe other hand, when the transmission is in high gear, the circuit maybe completed only through the wind switch 6i,

and therefore, under such conditions it is the wind switch that controlsthe automatic clutch operating means.

Figs. 1 and 2 illustrate conditions and the relative positionsof theparts of the clutch control means when the vehicle is being operated inlow gears and the clutch is operated automatically. It will be. notedthat under such conditions the high gear switch 58 is closed and theelectric circuit is completed therethrough. This causes the solenoidvalve 46 to remain open and, therefore, the movements of the wind switchii are immaterial. The clutch control means respond only to themovements of the valve 42 controlled by the accelerator pedal 43. If thepedal 43 is released, the clutch is disengaged automatically. If, on theother hand, the pedal 43 is pressed down as shown in Fig, 2, the vacuumcommunication between the engine manifold and the power cylinder 35 isinterrupted, and the clutch is engaged by the action of the springs 25.It should be noted in this instance that provision of a slot 33a on thepiston rod 33 prevents entrapment of air in the cylinder 35, while asimi-- lar slot on the valve 42 admits air into the power By virtue ofsuch an arrangement cylinder 35 for equalizing the pressure at bothsides of the piston 31.

If under the conditions illustrated in Fig. 2, the accelerator pedal 43is released for shifting into high gear, the respective positions of theclutch control means become as indicated in Fig. 4: the high gear shiftrail 18 moves forward and opens the high gear switch 56, the wind switchis closed, the electric circuit is closed through the wind switch,causing the solenoid valve 46 to open. The clutch is still disengaged.If, however, the pedal 43 is pushed down for regular driving at speedsnot exceeding twenty miles per hour, the valve 42 will move to interruptthe vacuum communication and to permit a firm engagement of the clutch.Thus when the vehicle is operated in high gear at speeds below twentymiles per hour, the solenoid valve is firmly held open, and thereforethe automatic clutch control means operate in response tov the releaseof the accelerator pedal 43.

However, as the vehicle increases its speed to the predetermined speed,such as twenty miles per hour, the velocity of the air in the air streamproduced by the fan becomes suflicient to shift the vane 35 rearwardly,thus breaking the circuit, in consequence whereof the valve 43 ispressed down on its seat by the spring 41, interrupting the vacuumcommunication between the engine manifold and the power cylinder 35, andrendering the valve 42 inoperative. Such conditions are illustrated inFig. 3. Thus, on vehicle speeds above the predetermined speed, movementsof the valve 42 are immaterial, since the vacuum communication ispermanently interrupted by the solenoid valve 46. In other words, atspeeds above the set speed the clutch control means do not respond tothe release of the accelerator pedal 43.

If under such conditions the brakes are suddenly applied causing rapiddeceleration of the vehicle, the inertia of the vane 65 will cause it tocontinue its forward movement, thereby cl0sing the wind switch. Theclosing of the wind switchjl will complete the circuit therethrough,causing opening of the valve 46 as shown in Fig. 4. Since under suchconditions the accelerator pedal 43 is released, there is a freecommunication between the intake manifold of the engine and the powercylinder 35. Hence, the vacuum existing in the manifold is permitted toact on the piston 31, thereby disengaging the clutch. Closing of thewind switch BI is accomplished practically momentarily and, therefore,the clutch is disengaged before the engine is stalled. It is importantto note that since the closing force developed in the switch because ofthe inertia of the vane 65 depends primarily upon the rate 01'deceleration of the vehicle and not directly upon the speed at which thevehicle is traveling at the moment of application of brakes, closing ofthe switch may be effected above the speed at which the switch normallycloses, that is above the speed of twenty miles per hour in the presentembodiment, whereby sufiicient time is given to the clutch controlmechanism to function and to effect disengagement of the clutch beforethe vehicle comes to rest. By proper selection of the weight anddimensions of the vane, it is possible to produce a switch which wouldclose at any speed above the predetermined speed upon the suddenapplication of brakes.

Figs, 9 to 12 inclusive show a modified form of the wind switch in whichmagnetic means are employed to prevent hesitation of the vane 65.

lilaid means are exemplified by a magnet 19 mounted on the bracket IIIto which bracket a casing 8| is secured by means of a bolt 82. Themagnet I! cooperates with a cam bracket 83 having extensions 83a and 83badapted to bc'pulled toward the magnet by the magnetic action thereoi.The cam bracket 83 is provided with a pinrality of notches similar tothe notches 69 of the cam 10 oi the preferred form of the switch andserving the same purpose. A conductor II is provided for the purpose ofensuring constant electric contact between the cam bracket 83 and theplate or bracket 80. The magnet 19 may serve also as means for limitingthe worklog stroke of the vane 65. However, it may be desirable undercertain conditions to decrease the initial force necessary to move theportions 83a and 83b from the magnet when they are in actual contacttherewith. This may be done by an ad- ,iustable cam 85 secured on thebolt 82 by means oi a second nut 82a, the cam 85 being so shaped thatrotation thereof on the bolt 82 permits adjustment oi the working strokeof the vane 65. A bracket portion 86 may be bent in order that theportion 83a comes in contact with it just heiore the portion 83b touchesthe magnet. The electric contact is established or broken by means oitwo contact pieces, one of them carried by the extension 830 while theother is secured to a resilient strip 81 riveted or otherwise secured tothe bracket I but electrically insulated therei'rorn. Operation of thewind switch so constructed is substantially similar to that of thepreierred form and no special detailed explanation tliereoi is deemednecessary.

Thus, considered from one of its broader aspects my inventioncontemplates providing improved control means for an automatic clutch,whereby automatic action of the clutch is ensured in the lower gears andin high gear at vehicle speeds below twenty miles per hour, abovewi'iich speed the conventional operation of the clutch is reestablished.In addition, disengaget of the clutch by automatic means is end when thebrakes are suddenly applied at of the vehicle speeds, the response ofthe tioizis practically momentary.

clarion:

l. in a motor vehicle having an engine with an intake manifold. aclutch, a transmission and riven by the engine; a clutch controlinehanism comprising a clutch operating vacuum cylinder operativelyconnected with said manifold, an electric circuit including a source ofelectric energy, a solenoid controlled valve electrically connected tosaid source and adapted to control the connection between said manifoldand said cylinder, and a switch operated by the stream produced by thefan, said switch being electrically connected to said source and to saidsolenoid controlled valve and being adapted to be closed when thevehicle is being operated below a predetermined speed, therebycompleting the circuit and. energizing said solenoid controlled valve.

in a motor vehicle having an engine with an intake manifold, a clutch, atransmission and ion driven by the engine: a clutch control mechanismcomprising a clutch operating vacuum. cylinder operatively connectedwith said manifold, an electric circuit including a source 0! clutch.control means being under such condielectric energy, a solenoidcontrolled valve electrically connected to said source and adapted tocontrol the connection between said manifold and said cylinder, and aswitch operated by the air stream produced by the fan, said switch beingelectrically connected to said source and to said solenoid controlledvalve and being adapted to be closed when the vehicle is being operatedin direct gear below a predetermined speed, thereby completing thecircuit and energizing said solenoid controlled valve to open the vacuumconnection between the engine manifold and clutch operating cylinder.

3. In a motor vehicle having an engine with an intake manifold, aclutch, a transmission and a fan driven by the engine; a clutch controlmechanism comprising a clutch operating vacuum cylinder operativelyconnected with said manifold, an electric circuit including a source ofelectric energy, a solenoid controlled valve electrically connected tosaid source and adapted to control the connection between said manifoldand said cylinder, and a switch operated by the air stream produced bythe fan, said switch being electrically connected to said source and tosaid solenoid controlled valve, said switch adapted to be closed whenthe vehicle is being operated in direct gear below a predetermined speedand to be opened when the vehicle is being operated above said speed,said switch being further adapted to be closed by the inertia of itsparts when brakes are applied at a vehicle speed exceeding saidpredetermined speed.

4. A clutch control mechanism for a motor vehicle having an engine withan intake manifold, a fan driven by said engine, and a clutch; saidmechanism comprising a cylinder and a vacuum operated piston thereinoperatively connected with said clutch, said piston adapted to disengagethe clutch when acted upon by vacuum; a vacuum connection between saidcylinder and the intake manifold of the engine; means interrupting saidvacuum connection when the accelerator pedal is actuated; a mainelectric circuit including a source of electric current and a solenoidvalve having a winding electrically connected to said source, said valveadapted to interrupt said vacuum connection when said circuit is broken.

5. A clutch control mechanism for a motor vehicle having an engine withan intake manifold, a fan driven by said engine, and a clutch; saidmechanism comprising a cylinder and a vacuum operated piston thereinoperatively connected with said clutch, said piston adapted to disengagethe clutch when acted upon by vacuum; a vacuum connection between saidcylinder and the intake manifold of the engine; means interrupting saidvacuum connection when the accelerator pedal is actuated; a mainelectric circuit including a source of electric current and a sole noidvalve having a winding electrically connected to said source, said valveadapted to interrupt said vacuum connection when said circuit is broken,and a parallel sub-circuit electrically connected to said main circuit,said sub-circuit including a switch adapted to be opened by the actionof the air stream produced by the fan when the velocity of the airreaches a predetermined value, and to be closed when the velocity of theair falls below said value.

PAUL H. MAURER.

